Apache Point
Clear Sky Chart
History

This sumarizes the distribution of each different forecast outcome for the Apache Point clear sky chart from 2005-11-06 to 2024-11-06.

This page is a summary of past forecasts. Even though it's based only on forecasts, some people use these pages as clue to a site's climate. But climate data based on actual observation should be preferred (if you can find it!).

Cloud, Transparency and Seeing forecasts are summarized individually. But because good observing conditions require a combination of minimum cloud cover, transparency and seeing, the individual forecast summaries can be difficult to interpret. The observing conditions section counts the combinations of conditions needed for common types of astronomical observation.

Observing Conditions

The following tables count the occurrence of the combinations of forecast and darkness conditions needed for different observations. Conditions are rated by by what percentage of the hours the observation would likely be attempted are usable.

Observation Type	Minimum conditions for hour to be usable				Out of hours
	Clear of Clouds	Transparency	Seeing	Sky Brightness
Planetary:	50%	(no limit)	Average	(no limit)	Nighttime Hours
Deep Sky:	70%	Average	(no limit)	5.9	Nighttime Hours
CCD Imaging:	70%	Below Average	Poor	(no limit)	Nighttime Hours

Percentages are of nighttime hours per month, or per year, when a particular observing conditions was met. Deep Sky percentages never exceed 50% because the moon is up half the time. Deep sky percentages are much lower for charts at high latitudes because of fewer dark hours in the summer.

Overall

By Month

Individual Forecasts

The length of each colored bar in the "occurrence of each Forecast" column is proportional to the number of times the chart forecast that color. The percentages are of the total number of hours per month, or per year, with a particular forecast. The colors as the same as those used in clear sky charts.

Note: Transparency probabilities are only counted for those hours that have 30% or less cloud cover. Seeing probabilities are only counted for those hours that have 80% or less cloud cover. If that's too tricky, try Observing Conditions instead.

Overall

		Occurrence of each Forecast	Data Points
Cloud Cover	Day	4 5% 2 5% 4 4 4 4 6% 7% 57%	104327
	Night	5% 5% 2 5% 3 3 4 3 5% 7% 59%	103439
Transparency	Day	23% 5% 10% 17% 25% 20%	104092
	Night	23% 4 9% 16% 27% 21%	103264
Seeing	Day	10% 19% 28% 25% 15% 4	14659
	Night	8% 13% 26% 31% 18% 3	24896

By Month

Percentage Cloud Cover SW (2006-)
Color Meanings: Overcast 90% covered 80% covered 70% covered 60% covered 50% covered 40% covered 30% covered 20% covered 10% covered Clear
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	2 11% 4 7% 3 3 3 3 6% 5% 53%	2858
	11th to 20th	Day	3 5% 2 5% 3 2 3 2 4 5% 67%	2860
	21st to end	Day	8% 13% 4 5% 3 3 4 5% 5% 5% 45%	3146
February	1st to 10th	Day	5% 7% 1 4 2 3 3 2 4 6% 63%	1860
	11th to 20th	Day	7% 7% 2 4 4 3 3 2 5% 5% 58%	1849
	21st to end	Day	5% 7% 2 4 4 2 3 2 3 5% 64%	1570
March	1st to 10th	Day	4 8% 2 5% 3 3 3 3 3 6% 59%	3314
	11th to 20th	Day	4 7% 2 6% 3 3 3 3 4 6% 58%	3490
	21st to end	Day	2 10% 3 7% 5% 4 4 4 5% 7% 50%	3965
April	1st to 10th	Day	3 4 1 4 3 3 4 3 5% 6% 64%	2280
	11th to 20th	Day	3 4 2 4 3 2 2 2 3 5% 70%	2251
	21st to end	Day	3 3 1 3 2 2 2 3 4 5% 71%	2280
May	1st to 10th	Day	2 3 1 3 2 2 2 2 2 4 78%	3800
	11th to 20th	Day	2 3 1 3 3 3 3 3 5% 6% 68%	3765
	21st to end	Day	1 2 1 2 1 1 2 2 3 5% 80%	4345
June	1st to 10th	Day	3 4 1 3 3 4 4 4 6% 8% 60%	2660
	11th to 20th	Day	3 2 1 2 2 3 3 4 5% 6% 68%	2660
	21st to end	Day	4 4 2 5% 5% 5% 6% 6% 8% 9% 45%	2559
July	1st to 10th	Day	5% 4 2 6% 5% 6% 6% 5% 9% 12% 39%	4110
	11th to 20th	Day	3 3 1 5% 5% 6% 8% 7% 9% 12% 40%	4110
	21st to end	Day	9% 5% 2 7% 5% 7% 7% 7% 11% 11% 29%	4434
August	1st to 10th	Day	4 3 1 6% 4 7% 8% 7% 10% 11% 40%	3784
	11th to 20th	Day	4 4 2 6% 5% 6% 7% 6% 9% 10% 41%	3726
	21st to end	Day	5% 4 2 8% 6% 6% 7% 7% 8% 11% 36%	4180
September	1st to 10th	Day	9% 6% 2 8% 5% 5% 6% 4 6% 8% 41%	2280
	11th to 20th	Day	9% 4 2 5% 5% 4 5% 4 6% 6% 52%	2280
	21st to end	Day	5% 3 2 4 3 2 3 4 6% 6% 62%	2095
October	1st to 10th	Day	4 3 2 5% 2 3 2 2 4 6% 67%	3172
	11th to 20th	Day	4 4 2 4 3 2 3 3 4 6% 65%	3150
	21st to end	Day	2 2 1 2 2 1 2 2 2 3 82%	3438
November	1st to 10th	Day	2 5% 2 4 2 2 2 3 4 6% 68%	1909
	11th to 20th	Day	4 3 2 3 2 3 4 3 5% 6% 66%	1758
	21st to end	Day	6% 6% 1 4 3 4 4 3 6% 6% 57%	1710
December	1st to 10th	Day	7% 7% 2 3 3 3 3 3 5% 7% 58%	1710
	11th to 20th	Day	6% 7% 3 7% 3 3 4 4 4 7% 52%	1969
	21st to end	Day	4 8% 2 3 3 3 3 3 4 5% 62%	3000
January	1st to 10th	Night	3 8% 3 7% 4 3 4 3 4 5% 57%	4097
	11th to 20th	Night	3 5% 1 3 3 4 4 2 3 5% 67%	4110
	21st to end	Night	7% 11% 2 7% 4 4 5% 4 5% 5% 45%	4521
February	1st to 10th	Night	4 8% 2 3 4 2 2 3 5% 6% 60%	2318
	11th to 20th	Night	9% 5% 2 4 3 3 3 3 4 6% 59%	2218
	21st to end	Night	5% 8% 2 4 2 3 4 3 5% 5% 60%	1884
March	1st to 10th	Night	4 6% 2 5% 3 2 3 3 4 6% 61%	3552
	11th to 20th	Night	8% 8% 2 5% 3 3 5% 3 5% 6% 53%	3490
	21st to end	Night	3 9% 2 7% 4 3 4 3 6% 8% 52%	3683
April	1st to 10th	Night	3 4 2 4 3 4 3 3 4 6% 65%	1900
	11th to 20th	Night	5% 4 2 4 3 3 3 3 4 6% 63%	1877
	21st to end	Night	4 3 1 4 2 2 3 2 4 5% 69%	1900
May	1st to 10th	Night	2 3 1 2 1 1 2 2 3 5% 78%	3170
	11th to 20th	Night	3 3 1 3 2 3 3 3 5% 5% 68%	3140
	21st to end	Night	1 2 1 2 1 2 2 2 3 4 81%	3217
June	1st to 10th	Night	2 4 2 5% 6% 4 4 4 6% 7% 56%	1520
	11th to 20th	Night	3 2 1 3 2 3 3 3 5% 8% 68%	1520
	21st to end	Night	3 5% 2 7% 6% 5% 4 5% 7% 9% 46%	1611
July	1st to 10th	Night	4 5% 2 7% 5% 6% 6% 5% 7% 10% 44%	2860
	11th to 20th	Night	3 2 1 5% 4 4 6% 5% 7% 11% 52%	2860
	21st to end	Night	5% 4 2 5% 4 6% 7% 7% 11% 13% 37%	3125
August	1st to 10th	Night	3 3 1 4 4 4 6% 5% 8% 15% 48%	3155
	11th to 20th	Night	4 3 1 4 3 4 4 4 7% 12% 55%	3113
	21st to end	Night	4 4 2 6% 5% 6% 7% 6% 9% 11% 39%	3487
September	1st to 10th	Night	6% 4 2 6% 5% 5% 5% 5% 6% 7% 49%	1900
	11th to 20th	Night	7% 3 2 5% 3 4 3 4 6% 6% 56%	1900
	21st to end	Night	4 3 1 4 3 3 4 4 4 6% 64%	2085
October	1st to 10th	Night	3 2 1 3 2 2 2 2 4 5% 74%	3793
	11th to 20th	Night	10% 4 1 4 2 2 2 2 3 4 66%	3778
	21st to end	Night	4 2 1 3 2 2 2 2 3 4 76%	4120
November	1st to 10th	Night	4 3 2 3 2 2 3 2 5% 7% 67%	2292
	11th to 20th	Night	3 2 1 3 2 3 3 4 4 6% 68%	2399
	21st to end	Night	7% 5% 2 5% 3 3 3 3 4 6% 59%	2470
December	1st to 10th	Night	8% 5% 2 4 3 3 3 4 5% 7% 56%	2470
	11th to 20th	Night	5% 6% 3 7% 5% 3 4 3 4 6% 54%	3223
	21st to end	Night	6% 7% 1 5% 3 3 3 2 4 5% 61%	4681

Transparency (when cloud cover <= 30%)
Color Meanings: Too cloudy to forecast Poor Below Average Average Above average Transparent
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	28% 2 11% 10% 35% 14%	2859
	11th to 20th	Day	18% 3 6% 18% 40% 15%	2860
	21st to end	Day	35% 3 10% 17% 24% 11%	3146
February	1st to 10th	Day	23% 3 5% 17% 27% 25%	1860
	11th to 20th	Day	27% 3 5% 15% 27% 23%	1859
	21st to end	Day	24% 1 4 9% 31% 31%	1570
March	1st to 10th	Day	24% 2 7% 8% 35% 23%	3314
	11th to 20th	Day	24% 4 7% 20% 29% 16%	3490
	21st to end	Day	29% 4 7% 13% 30% 18%	3965
April	1st to 10th	Day	18% 3 6% 15% 32% 26%	2280
	11th to 20th	Day	17% 2 5% 11% 30% 36%	2254
	21st to end	Day	16% 3 5% 13% 33% 30%	2280
May	1st to 10th	Day	12% 2 4 7% 25% 51%	3800
	11th to 20th	Day	15% 4 7% 11% 29% 34%	3768
	21st to end	Day	8% 2 3 11% 18% 58%	4345
June	1st to 10th	Day	17% 5% 9% 18% 27% 22%	2660
	11th to 20th	Day	14% 3 6% 13% 24% 40%	2660
	21st to end	Day	27% 8% 12% 16% 20% 16%	2559
July	1st to 10th	Day	30% 9% 22% 15% 15% 9%	4046
	11th to 20th	Day	28% 12% 19% 21% 17% 4	4041
	21st to end	Day	34% 14% 22% 21% 9% 1	4294
August	1st to 10th	Day	28% 12% 17% 31% 10% 2	3772
	11th to 20th	Day	28% 13% 16% 26% 15% 2	3762
	21st to end	Day	34% 11% 19% 25% 10% 1	4179
September	1st to 10th	Day	36% 7% 12% 16% 19% 10%	2280
	11th to 20th	Day	28% 6% 9% 19% 28% 10%	2280
	21st to end	Day	20% 5% 8% 21% 33% 14%	2095
October	1st to 10th	Day	17% 4 6% 15% 33% 24%	3172
	11th to 20th	Day	20% 3 7% 19% 32% 19%	3150
	21st to end	Day	10% 2 3 20% 36% 29%	3438
November	1st to 10th	Day	18% 3 4 21% 30% 23%	1909
	11th to 20th	Day	18% 3 7% 20% 28% 25%	1758
	21st to end	Day	24% 5% 6% 16% 30% 19%	1710
December	1st to 10th	Day	25% 3 6% 21% 30% 15%	1710
	11th to 20th	Day	30% 4 9% 16% 28% 14%	1967
	21st to end	Day	23% 2 5% 17% 30% 23%	3000
January	1st to 10th	Night	26% 2 10% 12% 33% 17%	4097
	11th to 20th	Night	19% 3 6% 14% 44% 13%	4110
	21st to end	Night	37% 3 9% 14% 26% 11%	4521
February	1st to 10th	Night	23% 3 7% 14% 26% 27%	2318
	11th to 20th	Night	26% 3 6% 13% 30% 23%	2218
	21st to end	Night	24% 3 5% 9% 28% 30%	1884
March	1st to 10th	Night	23% 2 6% 11% 35% 23%	3552
	11th to 20th	Night	27% 5% 9% 15% 29% 15%	3490
	21st to end	Night	26% 3 9% 13% 31% 17%	3683
April	1st to 10th	Night	20% 3 5% 11% 37% 24%	1900
	11th to 20th	Night	21% 3 6% 11% 27% 32%	1877
	21st to end	Night	17% 4 4 14% 33% 27%	1900
May	1st to 10th	Night	11% 2 3 6% 25% 54%	3170
	11th to 20th	Night	15% 4 8% 14% 23% 35%	3141
	21st to end	Night	9% 2 4 9% 19% 57%	3218
June	1st to 10th	Night	24% 5% 8% 16% 21% 25%	1520
	11th to 20th	Night	15% 3 5% 13% 23% 41%	1520
	21st to end	Night	29% 8% 13% 17% 15% 18%	1611
July	1st to 10th	Night	33% 6% 17% 20% 17% 7%	2815
	11th to 20th	Night	23% 8% 16% 28% 19% 6%	2806
	21st to end	Night	32% 10% 24% 23% 10% 1	3027
August	1st to 10th	Night	21% 9% 16% 34% 17% 3	3144
	11th to 20th	Night	20% 7% 13% 37% 20% 2	3143
	21st to end	Night	33% 9% 19% 25% 12% 2	3487
September	1st to 10th	Night	30% 7% 13% 16% 20% 14%	1900
	11th to 20th	Night	26% 6% 10% 18% 26% 14%	1900
	21st to end	Night	20% 5% 10% 17% 33% 15%	2085
October	1st to 10th	Night	14% 3 6% 13% 35% 30%	3793
	11th to 20th	Night	24% 3 5% 13% 36% 20%	3778
	21st to end	Night	14% 2 2 19% 31% 32%	4120
November	1st to 10th	Night	17% 3 4 17% 34% 25%	2292
	11th to 20th	Night	16% 3 6% 17% 33% 26%	2399
	21st to end	Night	26% 3 6% 15% 31% 20%	2470
December	1st to 10th	Night	26% 4 6% 17% 28% 19%	2470
	11th to 20th	Night	29% 3 9% 16% 24% 18%	3224
	21st to end	Night	25% 3 7% 13% 30% 22%	4681

Seeing (when cloud cover <= 80%)
Color Meanings: Too cloudy to forecast Bad 1/5 Poor 2/5 Average 3/5 Good 4/5 Excellent 5/5
Month	Days in Month		Occurrence of each Forecast	Data Points
January	1st to 10th	Day	17% 30% 26% 23% 4	270
	11th to 20th	Day	17% 28% 28% 21% 4 1	270
	21st to end	Day	11% 32% 30% 19% 8% 1	297
February	1st to 10th	Day	17% 26% 28% 21% 7% 1	270
	11th to 20th	Day	18% 33% 31% 14% 3	270
	21st to end	Day	25% 38% 21% 12% 3	225
March	1st to 10th	Day	19% 31% 35% 12% 3 1	376
	11th to 20th	Day	21% 28% 32% 13% 4 2	460
	21st to end	Day	19% 37% 32% 9% 2 1	506
April	1st to 10th	Day	13% 35% 35% 12% 2 2	460
	11th to 20th	Day	14% 39% 33% 11% 2	452
	21st to end	Day	13% 35% 33% 15% 2 1	460
May	1st to 10th	Day	8% 29% 45% 15% 3 1	463
	11th to 20th	Day	4 24% 44% 21% 6% 1	488
	21st to end	Day	6% 21% 46% 21% 6% 1	572
June	1st to 10th	Day	4 9% 30% 37% 17% 3	680
	11th to 20th	Day	3 10% 33% 33% 19% 2	680
	21st to end	Day	4 5% 27% 34% 26% 4	579
July	1st to 10th	Day	6% 3 15% 39% 27% 9%	486
	11th to 20th	Day	5% 2 10% 37% 37% 9%	484
	21st to end	Day	6% 2 9% 31% 42% 11%	531
August	1st to 10th	Day	3 2 10% 34% 38% 12%	487
	11th to 20th	Day	5% 5% 13% 39% 28% 9%	477
	21st to end	Day	6% 3 13% 35% 35% 9%	539
September	1st to 10th	Day	10% 5% 20% 37% 22% 6%	490
	11th to 20th	Day	7% 3 27% 40% 17% 6%	490
	21st to end	Day	7% 9% 31% 34% 13% 6%	305
October	1st to 10th	Day	10% 9% 32% 30% 16% 3	300
	11th to 20th	Day	9% 15% 32% 27% 12% 5%	300
	21st to end	Day	11% 18% 29% 23% 14% 4	330
November	1st to 10th	Day	9% 29% 34% 15% 9% 3	285
	11th to 20th	Day	6% 18% 31% 28% 13% 3	270
	21st to end	Day	14% 32% 26% 19% 9%	270
December	1st to 10th	Day	18% 25% 26% 23% 7% 1	270
	11th to 20th	Day	11% 36% 30% 18% 5%	270
	21st to end	Day	21% 30% 28% 16% 5%	297
January	1st to 10th	Night	10% 13% 30% 31% 13% 3	760
	11th to 20th	Night	10% 16% 29% 29% 13% 3	760
	21st to end	Night	11% 18% 28% 27% 14% 2	836
February	1st to 10th	Night	11% 17% 29% 28% 12% 3	760
	11th to 20th	Night	12% 21% 34% 25% 8% 1	744
	21st to end	Night	11% 27% 38% 19% 4 1	628
March	1st to 10th	Night	11% 25% 27% 27% 8% 1	760
	11th to 20th	Night	13% 17% 28% 29% 13% 1	760
	21st to end	Night	8% 24% 33% 25% 9% 1	755
April	1st to 10th	Night	6% 26% 38% 23% 7%	570
	11th to 20th	Night	10% 25% 33% 25% 6%	563
	21st to end	Night	8% 22% 37% 26% 7%	570
May	1st to 10th	Night	7% 18% 35% 31% 8%	570
	11th to 20th	Night	4 14% 32% 35% 15% 1	561
	21st to end	Night	5% 12% 36% 36% 10% 1	617
June	1st to 10th	Night	2 8% 27% 42% 19% 1	570
	11th to 20th	Night	4 8% 28% 39% 18% 2	570
	21st to end	Night	5% 7% 20% 41% 25% 3	570
July	1st to 10th	Night	5% 4 19% 41% 30% 3	555
	11th to 20th	Night	4 1 14% 37% 38% 5%	552
	21st to end	Night	6% 2 13% 33% 36% 10%	624
August	1st to 10th	Night	4 2 9% 29% 44% 11%	567
	11th to 20th	Night	5% 3 13% 28% 40% 11%	564
	21st to end	Night	4 4 13% 30% 40% 8%	627
September	1st to 10th	Night	6% 5% 16% 33% 34% 7%	570
	11th to 20th	Night	7% 2 16% 43% 27% 4	570
	21st to end	Night	5% 8% 21% 37% 26% 3	570
October	1st to 10th	Night	7% 7% 26% 37% 20% 3	753
	11th to 20th	Night	8% 7% 27% 33% 22% 4	760
	21st to end	Night	7% 11% 22% 28% 24% 7%	836
November	1st to 10th	Night	7% 13% 25% 27% 23% 5%	764
	11th to 20th	Night	5% 10% 24% 36% 21% 3	879
	21st to end	Night	11% 15% 25% 27% 17% 5%	950
December	1st to 10th	Night	12% 16% 24% 31% 15% 2	950
	11th to 20th	Night	12% 18% 33% 24% 12% 1	950
	21st to end	Night	14% 17% 29% 29% 10% 2	931

Page generated at 2024-11-03 11:19:03. Version ac07

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